The present invention generally relates to oxygen recovery and, more particularly, to apparatus and methods of oxygen recovery in closed environments.
In long duration manned missions to Mars, the Moon, asteroids, etc. carrying sufficient oxygen to provide for the needs of the crew is a critical obstacle. NASA believes that the only solution is a “closed loop” in which the carbon dioxide exhaled by crew members is chemically converted back to oxygen. This has been a NASA goal for a number of years, but an effective solution to the problem has not been discovered.
Current processes that are well known to those skilled in the art, and which are in use on the International Space Station (ISS) include the Carbon Dioxide Removal Assembly (CDRA) which recovers carbon dioxide from the atmosphere in the cabin, and the Oxygen Generation Assembly (OGA) which uses electrolysis of water to generate hydrogen and oxygen. A developmental Sabatier reactor is in evaluation on the ISS which uses the hydrogen from the OGA to reduce the carbon dioxide from the CDRA to methane and water. The water can then be sent to the OGA to make oxygen.
However, only 50% of the CO2 can be reduced, because the Sabatier reaction requires 4 moles of hydrogen, while the OGA reaction only generates 2 moles. This limits oxygen recovery to <50%. The hydrogen “wasted” in making methane must be recovered. Methane pyrolysis can be of limited use. Others have tried to accomplish methane pyrolysis using microwaves, among other techniques, but they generate mostly acetylene, rather than carbon, so the maximum possible hydrogen recovery is reduced.
Acetylene is both flammable and explosive. Generation of this gas requires that it be promptly vented for safety reasons. The quantities generated by these other technologies are significant, meaning that a significant gap in loop closure will be involved. Some prior processes generate carbon via either the Bosch or Boudouard reactions. However, because these reactions are catalytic, and the carbon accumulates on and fouls the catalyst, they must be cleaned periodically, generating carbon dust. Other processes directly generate carbon soot.
Dust and soot are particularly difficult to deal with in a zero gravity environment since they can foul or escape from filters, and because they represent both an inhalation hazard to people and a threat to equipment. Uncontrolled soot generation can clog reactors and tubes. Even if soot or dust is vented from the spacecraft, it can be damaging. Soot in the vicinity of the spacecraft may coat solar panels or other exterior structures. In a Mars habitat scenario, discharging soot may contaminate the environment near the habitat, interfering with experimentation or affecting the operation of other equipment.
As can be seen, there is a need for improved apparatus and methods to recover oxygen in closed and/or gravity-free environments such as deep space vehicles.